Combined detector oscillator circuit



rch 1936. D. GRIMES ET AL COMBINED DETECTOR OSCILLATOR CIRCUIT Filed April 1, 1953 affirm N R 0 v 055 E MM N E/., vfi ogm m .1 mm .A MM

Patented Mar. 17,1936

NITED STATES PATENT OFFICE COIVIBINED DETECTOR OSCILLATOR CIRCUIT David Grimes and William S. Barden, Grasmerc,

Staten Island, N. Y.,

assignors to Radio Cor- 11 Claims.

The present invention relates to frequency changer networks, and more particularly to an improved frequency changer circuit of the combined detector oscillator type.

An efficient combined detector oscillator circuit for superheterodyne receivers should operate without distortion. To accomplish this object it is necessary to operate the autodyne first detector in such a manner that the signal grid is never swung positive with respect to the electron emitter of the first detector tube.

Accordingly, it may be stated that it is one of the main objects of this invention to provide a frequency changer circuit, of the combined detector oscillator type, wherein the electrode circuits of the frequency changer are so constructed that there is left a margin for the signal to occupy without causing current to flow in the signal grid circuit of the detector oscillator tube.

It is another object of the present invention to provide an electron discharge tube with circuits whereby it'may function as an autodyne first detector, the tube including additional electrodes whereby the system includes an oscillator whose bias is amplitude controlled.

Another important object of the invention is to provide a combined detector oscillator circuit for a superheterodyne receiver, which circuit includes a tube having its electrodes connected to circuits providing signal, local oscillation, and beat frequency circuits, the tube, additionally, including at least one auxiliary electrode which cooperates with the cathode to provide a rectifier which functions to automatically control the bias of the signal grid of the tube in such a manner that the potential of the signal grid is never swung positive with respect to the cathode. Still other objects of the present invention are to improve generally the simplicity and efficiency of superheterodyne receivers, and particularly provide an economical and compact form of combined detector oscillator network for such a receiver, which is not only reliable in operation, but is economically manufactured and assembled. The novel features which we believe to be characteristic of our invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation 'will best be understood by reference to the following description taken in connection with the drawing in which we have indicated diagrammatically one arrangement whereby our invention may be carried into effect. In the drawing, the single figure represents in diagrammatic form a portion of the circuit of a superheterodyne receiver embodying one embodiment of the present invention.

Referring now to the accompanying drawing wherein there is shown in the figure in purely schematic fashion part of a superheterodyne receiver, it will be noted that the frequency changer network is disposed between a source of signals, and an intermediate frequency amplifier. The frequency changer network, or combined detector oscillator circuit, (also described as an autodyne first detector network), includes a multi-electrode electron discharge tube l between whose signal control grid 2, and cathode 3, is connected a tunable signal input circuit 4.

This signal input circuit comprises an inductance coil L and a variable tuning condenser C, the rotor plates of the condenser being grounded, and a radio frequency by-pass condenser the latter being connected between the grounded side of coil L and the grounded side of condenser C. A signal grid biasing resistor R is connected between one side of the coil L and. the grounded cathode circuit of tube I.

. The tube I comprises a pair of virtually independent electrode systems. These two systems, however, have in common the cathode 3. One of the electrode systems comprises the cathode 3, which is of the indirectly heated type, the signal control grid 2, the screen grid 2', the anode 5, and the suppressor grid 5. The suppressor grid is disposed between the screen grid 2 and the anode 5, the suppressor grid being maintained at cathode potential by connecting it to a point substantially the midpoint, .on the cathode 3. It is to be understood that the grids 2, 2' and 5', as well as the anode 5, are the usual cylindrical elements disposed co-axially with respect to the cathode 3. It will be recognized that the electrode system just described is of the well known pentode type.

The other electrode system comprises a portion of the emission surface of the cathode 3 and at least one auxiliary anode 6 disposed adjacent this emission surface. Actually the tube is provided with a pair of auxiliary anodes 6, 6'. It will be observed that these auxiliary anodes are not in the electron stream flowing through the grids 2, 2' and 5', and to the anode 5. The tube l is usually designated as being of the duplex diode triode type when the screen grid 2 and suppressor grid 5' are not included. However, in the present case a more apt designation is duplex diode pentode.

Except for the inclusion of the screen grid 2' and suppressor grid 5', the construction of tube- I may be of the same construction as shown in connection with a duplex diode triode tube disclosed and claimed by T. M. Shrader in application Serial No, 622,140, filed July 12, 1932. Functionally, the auxiliary anodes 6 and 6 cooperate with the emission surface adjacent them to provide a pair of diodes which is independent of the pentode system except for the common cathode sleeve, which has one emitting surface for the diode anodes and another for the pentode electrodes. structurally, and as shown in the aforementioned Shrader application, the two diode plates 6 and 6' are disposed around a portion of the cathode sleeve 3 which is not surrounded by the electrodes 2, 2', 5' and 5.

The anodes 6 and 6' are shown tied together so as to provide half wave rectification. The pentode anode 5 is connected to the positive terminal of the potential source B through a path which includes the tunable local oscillator circuit 1 and a network 8 resonant to the operating intermediate frequency. The negative terminal of the source B is connected to the grounded side of the resistor R. The local oscillation network comprises the oscillator coil L1 and the tunable condenser C1, and the network 8 includes the primary coil L2 of the intermediate frequency coupling transformer A, the coil L2 being shunted by the fixed condenser G2 which resonates the coil L2 to the operating intermediate frequency.

The grounded cathode lead of tube l includes in series therein the coil L3 which is magnetically coupled to the oscillator coil L1. The diode anodes 6 and 6' are connected to the ungrounded side of the bias resistor R through a lead which includes in series therein the coil L4, this coil being magnetically coupled to the oscillation coil L1. The screen grid 2 of tube l is connected by an adjustable lead H] to a point on the potential source B which is at a less positive potential than the point to which the anode 5 is connected.

The variable tuning condensers C and C1 have their rotors mechanically coupled together so that they may be operated by the usual single control means, shown by the dotted lines II, and it is to be clearly understood that the oscillation circuit I may include padding condensers so that the intermediate frequency produced across the network 8 is substantially constant regardless of the frequencies to which the circuits 4 and 1 are tuned. Such padding condensers are well known to those skilled in the art and are not shown in circuit 1 to preserve simplicity of disclosure. The intermediate frequency energy produced across the network 8 is impressed upon the input circuit l2 of the intermediate frequency amplifier, which input circuit is resonant to the intermediate frequency, and the output of this amplifier is then rectified in the usual second detector, and ultimately utilized in any well known fashion.

It is believed that the operation of the present invention will now be more clearly understood. The source of signals, which is coupled to the coil L, may be the usual antenna circuit, or can even be one or more stages of tuned radio frequency amplication. In any event, the signal circuit 4 is tuned to the incoming signal, while the circuit 7 fixes the local oscillation frequency. The coupling M between coils L1 and L3 augments oscillation, and causes a signal grid swing value, say E1. The coil L4 being magnetically coupled to the oscillator coil L1, results in the production of an additional signal grid swing value. say E2. The polarities of these two couplings are to be such that E1 and E2 are in phase relative to the diode anode 6 and 6'.

Therefore, assuming efiiciency from the diode rectifier, the direct current voltage across the resistor R is a peak E1 plus peak E2. If E: is finite, the direct current bias across resistor R (this is the control grid bias of the oscillator) must then exceed the peak swing on the grid E1, as desired, thereby leaving a margin for the signal to occupy without causing grid current. The bias resistor R may have a value of about 0.5 megohm; the condenser 5" may have a value of 0.1 or 0.01 mfd.

While we have indicated and described a system for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of our invention as set forth in the appended claims.

What we claim is:

1. A self-biased autodyne first detector circuit comprising, an electron discharge tube provided with a pair of independent electrode systems having a common cathode, one of said electrode systems including a grid electrode, circuits electrically connected with the last named electrode system to provide signal input, local oscillation, and beat frequency circuits, local oscillations being produced by feeding back a voltage from the local oscillation circuit to the grid of the tube, the other electrode system being electrically connected with said local oscillation circult and said signal circuit and providing a circuit for rectifying currents developed in said local oscillation circuit, the voltage fed to the rectifying circuit from the local oscillation circuit being greater than the voltage fed back from the local oscillation circuit to the grid of the tube by an amount which is normally suflicient to insure a marginal bias on the grid of the tube for the signals to occupy to thereby preclude grid current.

2. In an autodyne first detector circuit, an electron discharge tube provided with a pair of independent electrode systems having a common cathode, one of said electrode systems including a grid electrode, circuits electrically connected with the last named electrode system to provide signal input, local oscillation, and beat frequency circuits, local oscillations being produced by feeding back a voltage from the local oscillation circuit to the grid of the tube, the other electrode system being electrically connected with said local oscillation circuit and said signal circuit and providing a circuit for rectifying currents developed in said local oscillation circuit, an impedance disposed in said rectifier circuit for developing a proper biasing potential for the signal control electrode of said first named electrode system, the voltage fed to the rectifying circuit from the local oscillation circuit being greater than the voltage fed back from the local oscillation circuit to the grid of the tube whereby the grid bias always exceeds the radio frequency voltage impressed upon the grid.

3. In an autodyne first detector circuit, an electron discharge tube provided with a pair of independent electrode systems having a common cathode, one of said electrode systems including signal control and grid electrodes, circuits electrically connected with the last named electrode system to provide signal input, local oscillation, and beat frequency circuits, local oscillations being produced by feeding back a voltage from the local oscillation circuit to the grid of the tube, the other electrode system being electrically connected with said local oscillation circuit and said signal circuit and providing a circuit for rectifying currents developed in said local oscillation circuit, a resistor in said rectifier circuit having a magnitude such that a negative potential is constantly applied to the signal control electrode of said first named electrode system, the voltage fed to the rectifying circuit from the local oscillation circuit being greater than the voltage fed back from the local oscillation circuit to the grid of the tubewhereby the grid bias always exceeds the radio frequency voltage impressed upon the rid.

4. In an autodyne first detector circuit, an electron discharge tube provided with a pair of in-' dependent electrode systems having a common cathode, one of said electrode systems including a grid electrode, circuits electrically connected with the last named electrode system to provide signal input, local oscillation, and beat frequency circuits, local oscillations being produced by coupling between the local oscillation circuit and the tube input whereby a voltage is fed from the local oscillation circuit to the grid of the tube, the other electrode system being electrically connected with said local oscillation circuit and said signal circuit and providing a circuit for rectifying currents developed in said local oscillation circuit, the voltage fed to the rectifying circuit from the local oscillation circuit being greater than the voltage fed back from the local oscillation circuit to the grid of the tube whereby the grid bias always exceeds the radio frequency voltage impressed upon the grid, said first named electrode system including a positive screen grid and a suppressor grid, at cathode potential, disposed between the positive screen grid and the more positive anode, and said second named electrode system including at least one auxiliary anode disposed adjacent said common cathode outside the electron stream passing through said screen grid and suppressor grid.

5. In an autodyne first detector circuit, an electron discharge tube provided with a pair of independent electrode systems having a common cathode, one of said electrode systems including a grid electrode, circuits electrically connected with the last named electrode system to provide signal input, local oscillation, and beat frequency circuits, local oscillations being produced by feeding back a voltage from the local oscillation circuit to the grid of the tube, the other electrode system being electrically connected with said local oscillation circuit and said signal circuit and providing a circuit for rectifying currents developed in said local oscillation circuit, and an impedance disposed in said rectifier circuit for developing a proper biasing potential for the signal control electrode of said first named electrode system, the voltage fed to the rectifying circuit from the local oscillation circuit being greater than the voltage fed back from the local oscillation circuit to the grid of the tube by an amount which is normally sufi'icient to maintain a grid bias margin for the signals to occupy without causing a flow of grid current, said first named electrode system including a positive screen grid and a suppressor grid, at cathode potential, disposed between the positive screen grid and the more positive anode, and said second named electrode system including at least one auxiliary anode disposed adjacent said common cathode outside the electron stream passing through said screen grid and suppressor grid. 1

6. In an oscillator detector circuit an electronic tube provided with a pair of independent electrode systems having a common cathode one of said electrode systems having circuits electrically connected thereto to provide input and output circuits for said system comprising signal input, local oscillation and beat frequency circuits, said input circuit thereof being linked with the output circuit to facilitate the transfer of energy from the output circuit to the input circuit for producing oscillations, the other electrode system being electrically connected with thelocal oscillation circuit and said signal circuitand providing a circuit for rectifying currentsdeveloped in the local oscillation circuit, the energy fed to the rectifying circuit being of a higher voltage than the voltage of the energy fed back from' the output circuit to the input circuit whereby "the grid bias always exceeds the radio frequency voltage impressed upon the grid,

7. In an oscillator detector circuit an electronic tube provided with two independent electrode systems having a common cathode the first of said n electrode systems having circuits electrically connected thereto to provide input and output circuits for the first system, said circuits including signal input, local oscillation and beat frequency circuits, a coupling between the input circuit and the local oscillation circuit to facilitate the transfer of energy from the local oscillation circuit to the input circuit for producing oscillations, a coupling circuit between the second electrode system and the local oscillation circuit, said two coupling circuits being electrically in series with respect to the second electrode system, the second electrode system providing means for rectifying currents developed in the local oscillation circuit and transferred to the second electrode system through said two series coupling circuits, a resistor connected both in said input circuit and in the rectifier electrode system circuit for developing a proper biasing potential for one of the electrodes of the first electrode system.

8. In an autodyne first detector circuit an electron discharge tube provided with a pair of independent electrode systems having a common cathode, one of said electrode systems having circuits electrically connected therewith to provide signal input, local oscillation and beat frequency circuits, the other electrode system comprising at least one anode and the common cathode acting as a diode rectifier, connections external said tube for connecting the cathode to the diode rectifier including a coupling element, a bias resistor and a second coupling element all in series, said two coupling elements being coupled to the local oscillation circuit and arranged so as to transfer energy from the local oscillation circuit to the rectifier circuit in phase with respect to the other electrode system and means for connecting said bias resistor in said signal input circuit whereby the potential drop across the bias resistor due to the flow of rectified current therein is utilized to bias an input electrode of the first electrode system.

9. A self-biased oscillation generator comprising an electronic tube provided with an input and an output circuit, said two circuits being linked to facilitate feeding back a, voltage from the output circuit to the input circuit for producing oscillations, a biasing impedance in said input circuit, means for producing a flow of direct current through said impedance compristifier in series, said last named circuit being linked to said output circuit whereby a voltage is impressed upon the rectifying circuit from the output circuit to thereby cause a flow of unidirectional current through said impedance, the voltage impressed upon the rectifier circuit being greater than the voltage fed back to the input circuit whereby the bias potential applied to the tube always exceeds the radio frequency voltage impressed upon the input circuit thereof.

10. An arrangement for generating high frequency oscillations comprising a thermionic tube provided with anode, cathode and control electrode, an oscillatory circuit associated with said tube, a controlling circuit associated with said control electrode, means for transferring energy from the oscillatory circuit to the controlling circuit for producing sustained electrical oscillations in the output circuit, a rectifier system, means including said first named means and an additional means for supplying high frequency energy to the rectifier system from the oscillatory circuit, said twomeans acting to supply said energy to the rectifier circuit in additive sense and means for using the potential derived from said rectifier to provide a bias voltage for the tube.

11. In an oscillator detector circuit, an electron tube provided with a pair of independent electrode systems having a common cathode, the first of said electrode systems having circuits ing a circuit including the impedance and a rec electrically connected thereto to-provide input;

the second electrode system through said two,

coupling means, said two coupling means being arranged with respect to the second electrode system so as to transfer energy from the local oscillation circuit to the rectifier circuit in phase as regards the second electrode system, and a re-;

sistor connected both in the input circuit and in the rectifier electrode system circuit for developing a proper biasing potential for one of the electrodes of the first electrode system, the drop across the bias resistor being substantially equal to the sum of the two peak values of the energy transferred to the rectifier electrode system through said two couplings.

DAVID GRIMES. WILLIAM S. BARDEN. 

